Encapsulated breakers, compositions and methods of use

ABSTRACT

An encapsulated breaker is enclosed within a hydrolytically degradable polymer coating. Compositions containing this encapsulated breaker, methods of making and methods of use are also described.

FIELD OF INVENTION

[0001] This invention relates to encapsulated breakers. Morespecifically, this invention relates to breakers that are encapsulatedwith a hydrolytically degradable material, and compositions and methodsfor using same.

BACKGROUND OF THE INVENTION

[0002] Hydraulic fracturing of subterranean formations is a well knowntechnique for increasing the permeability of such formations in therecovery of materials, such as petroleum products. In this technique, aviscous fluid (“fracturing fluid,” commonly an aqueous fracturing fluid,most commonly guar) is introduced to the wellbore, pressure is appliedto induce fracture, and proppants in the fluid (most commonly sand)maintain the fractures in an open state. The viscous fluid must then beremoved, and oil is harvested from the thus opened subterraneanformation. In order to facilitate the quick removal of the fracturingfluid, chemicals are used to reduce or “break” the viscosity of thefracturing fluid; these chemicals (most commonly oxidizers, and inparticular persulfates) are known as “breakers.” The chemical reactionof the breaker with the fracturing fluid is undesirable prior tocompletion of the fracturing operation. Therefore, it is advantageous toencapsulate or coat the particles with a polymer to delay the release ofthe breaker, and hence to delay the breaking of the fracturing fluid.

[0003] Many materials have been used in the art to encapsulate breakersfor fracturing fluids. For example, U.S. Pat. No. 4,506,734 (Nolte)describes a breaker within a crushable glass or ceramic coat thatruptures upon closure of the induced fractures. U.S. Pat. No. 4,741,401(Walles, et.al.) teaches that a polymer can be applied to a solidbreaker chemical, most preferably by air suspension coating. Thepolymers of Walles are most typically homopolymers and copolymers ofpolyolefin and ethylene oxides. This patent describes the release of thebreaker by rupture of the membrane, either by the force of closure ofthe fractures within the subterranean formation or by the osmoticpressure of water diffusing into the shell. In U.S. Pat. No. 5,164,099(Gupta, et.al.), a polymer is applied to a solid particle of a breakerchemical by interfacial polymerization. Typically, this polymer is apolyamide or a crosslinked cellulosic material. This patent states thatbreaker is released from the capsules described therein by diffusionthrough the membrane of the encapsulation.

[0004] U.S. Pat. No. 5,591,700 (Harris, et.al.) relates to encapsulatedbreakers that are coated by surfactants that are solid at ambientsurface conditions and which dissolve at elevated temperatures in thesubterranean formation. The surfactants are mixed in from the dry state.

[0005] Alkyl-2-cyanoacrylate monomers polymerize immediately in theepresence of a weak base, and as such have been widely used forencapsulation and particle coating in the pharmaceutical industry,primarily for the purpose of drug delivery.

[0006] For example, Kante et al. (Int. J. Pharm., 1980, 7, 45.) havedescribed a method for preparing actinomycin D nanoparticles usingpoly(butylcyanoacrylate).

[0007] U.S. Pat. No. 4,452,861 (to RCA Corporation) describes a methodfor coating luminescent, inorganic phosphors using polymericcyanoacrylates. The procedure outlined involves a five stage processwhich requires complete evaporation of the nonaqueous solvent duringeach of the coating stages and a final step which calls for washing ofthe coated particles.

SUMMARY OF THE INVENTION

[0008] An encapsulated breaker is provided for reducing the viscosity ofa fracturing fluid. The breaker is enclosed within a hydrolyticallydegradable polymer coating. Compositions containing this encapsulatedbreaker and methods of use are also described.

BRIEF DESCRIPTION OF THE DRAWING

[0009]FIG. 1 is a photograph of two vials of encapsulated breakercompositions in water, one vial containing encapsulated breaker of thepresent invention and the other containing encapsulated breaker coatedwithin a polymer that does not hydrolytically degrade. These vials havenot been heated.

[0010]FIG. 2 is a photograph of the vials of FIG. 1 after heating.

[0011]FIG. 3 is a graph showing the viscosity/time profile of guarcompositions containing no breaker, unencapsulated breaker andencapsulated breaker.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The encapsulated breaker of the present invention is enclosedwithin a hydrolytically degradable polymer coating. By “hydrolyticallydegrade” is meant that the polymer coating will react with water tochemically break down the polymer coating to predominantly non-solidcomponents in a time and temperature range appropriate for the intendeduse. Preferably, the coating will hydrolytically degrade within fourhours at 70° C. An encapsulated breaker having a coating thathydrolytically degrades is superior to prior art systems, because itallows better control of release time and ease of handling notpreviously afforded by prior art systems. Because the breaker isencapsulated in a material that reacts with water, rather than simplydissolves or dissipates in water, the release can be controlled throughthe reaction rate of the coating with water. Because the coating of thepresent invention partially or completely degrades by reaction withwater, the present invention can provide complete delivery of thebreaker.

[0013] Preferably, the encapsulated breaker of the present invention isrelatively stable at ambient temperatures. Thus, the encapsulatedbreaker does not reduce viscosity lower than 50% at 5 hours at roomtemperature (20-25° C.) in a Standard Breaking Test. The breaker is,however, released in a controlled manner at a later time in the breakingoperation. Thus, preferably the encapsulated breaker does not reduceviscosity lower than 50% at 70° C. at a first predetermined timeselected between fifteen minutes and 12 hours. This time period allowsthe fracturing operation to take place downhole. The encapsulatedbreaker does reduce viscosity lower than 50% at a second predeterminedtime period selected between fifteen minutes and 12 hours at 70° C. in aStandard Breaking Test, which occurs after the first predetermined time.Preferably, the first predetermined time is between about 2 and 3 hoursand the second predetermined time period is between about 3 and 5 hours.Further, the encapsulated breaker reduces viscosity lower than 50% in aStandard Breaking Test at least 20 minutes after the time that a likecomposition takes to reduce viscosity below 50% in a Standard BreakingTest where the breaker is not encapsulated. Preferably, the encapsulatedbreaker reduces viscosity at least 60 minutes later than a likecomposition with a non-encapsulated breaker.

[0014] Surprisingly, the coating for the breaker of the presentinvention substantially or completely dissipates under conditions of usein the subterranean system. Because no further microcapsule shell ispresent, or a substantially reduced amount of microcapsule shell ispresent, clean up of the well and recovery of the petroleum products issubstantially eased. Preferably, no more than 50% by weight of the shellremains as a solid component after exposure of the microcapsule to waterat 70° C. for four hours. More preferably, no more than 20% of the shellremains, and most preferably, no more than 5% remains as a solidcomponent after exposure of the microcapsule to water at 70° C. for fourhours.

[0015] Typically, the fracturing fluid is a hydrated polymer such asguar, hydroxyalkylguar, hydroxyalkylcellulose, carboxyalkylhydroxyguar,carboxyalkylhydroxyalkylguar, cellulose or other derivatized cellulose,xanthan and the like in an aqueous fluid to which is added a suitablecrosslinking agent. Suitable crosslinking agents include compounds suchas borates, zirconates, titanates, pyroantimonates, aluminates and thelike.

[0016] The polymer shell material of the present invention is primarilya poly(alkyl-2-cyanoacrylate), which is present in an amount sufficientto allow the boating to hydrolytically degrade at temperatures of useabove room temperature. Preferably, the poly(alkyl-2-cyanoacrylate) isat least about 50% by weight of the total content of the coating, morepreferably at least about 70% and most preferably at least about 90%.

[0017] Other materials that may be incorporated into the coating of thepresent material include comonomers that are copolymerizable withalkyl-2-cyanoacrylate. In particular, comonomers are vinyl reactivemonomers, such as those possessing α,β-unsaturated carbonylfunctionalities. Preferably, the comonomers are the esters of acrylicacid and methacrylic acid. A combination of different hydrophobicmonomers can be used and may include acrylic or methacrylic esters ofnon-tertiary alcohols, which have 1 to 14 carbon atoms, preferably from2 to 12 carbon atoms. It is preferred that the non-tertiary alcohol isan alkanol. Suitable alkanols to form the ester are alkanols such asethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol,2-pentanol, 3-pentanol, 2-methyl-1-butanol, 1-hexanol, 2-hexanol,2methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol,3,5,5-trimethyl-1hexanol, 3-heptanol, 1-octanol, 2-octanol, iso-octanol,2-ethyl-1-hexanol, 1decanol, 1-dodecanol, 1-tridecanol and1-tetradecanol. In addition, acrylamides such as t-butylacrylamide,t-octyl acrylamide, and N,N-dimethyl acrylamide can also be utilized.Finally, styrene and derivatives such as p-methoxystyrene can also beemployed as comonomers.

[0018] The preferred breaker material for aqueous-based fracturingfluids can comprise, for example, enzymes such as hemicellulase,oxidizers such as sodium or ammonium persulfate, organic acids or salts,such as citric acid or a citrate, fumaric acid, liquids adsorbed on asolid substrate, solid perborates, solid peroxides or other oxidizers,mixtures of two or more materials and the like. Most preferably, thebreaker material is potassium persulfate. For gelled hydrocarbonfracturing fluids, preferred breakers include calcium oxide, calciumhydroxide, p-nitrobenzoic acid, triethanolamine, sodium acetate, sodiumbicarbonate and the like.

[0019] Preferably, the coated breakers of the present invention areprovided in a slurry with an organic solvent that is compatible with thesubterranean system. Providing the coated breaker in a slurrycomposition offers significant advantages over dry breaker products.Specifically, encapsulated breaker slurries are easier to mix and pump.Additionally, surfactants may be incorporated in the slurry to assist inpreventing settling of the slurry.

[0020] The coated breaker particles are preferably provided in a solventthat does not facilitate the release of the breaker from its coating.Preferably, the solvent is substantially free of water if the solvent isthe reaction medium for preparing the coated particle. Preferredsolvents are non-hygroscopic solvents that provide a pumpable slurryunder conditions of use. Examples of preferred solvents include mineraloil (such as drill mud oil), vegetable oil, canola oil, siloxanes,hydrofluoroethers, mixtures thereof and the like. Materials arepreferably selected such that the material is pumpable even at freezingtemperatures. Aliphatic solvents may additionally be used, such asalkanes or aliphatic mixtures including kerosene. Preferably, thesolvent is selected such that the overall slurry has a flashpoint over93° C. for transport safety considerations as measured according to ASTMD 93-90 (the standard test methods for flashpoint by Pensky-Martens,closed tester.) In the case of solvents that have flashpoints that aretoo low, the effective flashpoint of the slurry composition may beadjusted by mixing solvents. Optionally, the particle may be provided ina dry format that may be mixed at the work site.

[0021] Optionally, the encapsulated breaker may be provided in an oilyor waxy medium to further control the time for release of the breaker.Access of water to the hydrolytically degradable capsule wall toinitiate hydrolytic degradation may be retarded because of the coatingof oil or wax. Optionally, the polymer that coats the breaker materialmay be chemically modified by selection of pendant functionality orsurface treatment of the coated breaker, so that the coated breaker hasan enhanced affinity to wet out an oily or waxy solvent. This furtheraffinity serves to provide additional short term protection of thecoating from contact with water. A mixture of solvents is particularlycontemplated in this embodiment, whereby a hydrophobic solvent that willhave an affinity to the coated breaker may be provided together with asolvent that is more hydrophilic. The presence of the more hydrophilicsolvent will serve to render the slurry more readily mixable with anaqueous fracturing fluid.

[0022] The breaker slurry composition may preferably contain asurfactant. Surfactants provide enhanced stability of the slurry andeven distribution of the particles suspended in the slurry. Preferredsurfactants include oxyalkylated phenolic resin surfactants, resin estersurfactants, polyol surfactants, alkylaryl sulfonate surfactants,polymeric amine surfactants, alcohol ether sulfonates, imidazolinecationic surfactants, complex phosphate esters, amine alkylarylsulfonates, alkyl amidoamine surfactants, polyamido imidazolinesurfactants, fatty imidazoline surfactants, dimer trimer acidsurfactants, polyoxyethylated rosin amines, polyoxyethylated rosinamines, polyoxyethylene glycol surfactants, alcohol ether sulfonatesurfactants, alcohol ether sulfate surfactants, sulfonate surfactants,sodium alpha olefin sulfonates, sodium alcohol ether sulfates, calciumalkylaryl sulfonates, amine dodecylbenzene sulfonates, fatty acidamides, alkanolamides, and mixtures thereof Such surfactants aregenerally known as petroleum surfactants, generally commerciallyavailable from Witco Company. Other surfactants include the fluorinatedsurfactants, such as Fluorad™ surfactants from 3M. Preferably, thesurfactant does not additionally contain water that might adverselyaffect the shelf life stability of the slurry.

[0023] Clays may be used in the slurry compositions of presentinvention, including smectic clays including modified montmorillonites,hectorites, and bentonites.

[0024] Proppants additionally may be provided in the slurry compositionto assist in holding the fractured subterranean formation open afterbreaking and removal of the fracturing fluid. Proppants may be selectedfrom any material appropriate for introduction downhole, including sandand sintered bauxite.

[0025] Thickeners may additionally be incorporated into the slurry.Preferred thickners include natural extracts such as gum arabic, gumghatti, khaya gum, agar, pectin, carrageenin and alginates; modifiednatural extracts; xanthan gums; modified cellulose, such as sodiumcarboxymethyl cellulose, methyl cellulose, and hydroxyalkylcelluloses;and synthetic polymers such as ultra high molecular carboxy vinyl(carbomers) and acrylic polymers.

[0026] The slurry composition comprising the encapsulated breaker mayadditionally comprise adjuvants suitable for incorporation in breakercompositions, such as colorants, fragrances, preservatives,anti-settling agents, pH controlling buffers, and viscosity modifiers.

[0027] The preferred coating of the present invention is produced bysuspending the core breaker particles in a non-aqueous liquid containingdissolved alkyl-2cyanoacrylate monomer. Polymerization of thealkyl-2-cyanoacrylate is effected on addition of a weak base, therebydepositing a coating on the particle surface. The present methodprovides both a high degree of coating efficiency, as well as excellentease of processing and isolation of the coated particles. A highlyefficient coating process is thereby achieved in a one step procedurewith no washing required.

[0028] In a preferred reaction of the present invention, potassiumpersulfate is suspended in a stirred solution of methyl-2-cyanoacrylateor ethyl-2-cyanoacrylate in non-aqueous solvent. As examples ofsolvents, aliphatic hydrocarbons such as hexane, heptane, and kerosenegive excellent results, while aromatic hydrocarbons such as toluene orxylene lead to poor results. Solvents containing a high degree ofmoisture cannot be used as the water will induce prematurepolymerization of the cyanoacrylate. After stirring for 5 to 10 minutesto effect thorough mixing, a drop of triethanolamine or other weak baseis added to initiate polymerization. Stirring is continued for a further30 minutes to ensure complete reaction at which time the coatedpotassium persulfate is collected by filtration and allowed to air dry.A coating efficiency of 93-98% is obtained, as determined by iodometrictitration.

[0029] Standard Breaking Test

[0030] An evaluation of the conditions of release of a breaker atconstant temperature is conducted as follows.

[0031] A guar gel was prepared by hydrating 25.11 g of gum guar (CASnumber 9000-30-0, purchased from the Aldrich Chemical Company) with 2.6L of water, in a 4 L vessel. On addition of 1.97 g of boric acid (usedas received from J.T. Baker Chemicals) the vessel was sealed and placedon rollers to rotate the entire vessel for 12 hours at about 20revolutions per minute to ensure mixing to a homogeneous fluid.Approximately 480 mL of the borate cross-linked guar fluid (viscosity ofca. 1800 cps) was added to a 500 mL Nalgene container. Subsequently,0.15 g of the encapsulated breaker (based on potassium persulfate) or asa comparison evaluation an unencapsulated breaker was added anddispersed throughout. The sample was then sealed to prevent water lossand placed into an oven (preheated to 60 ° C.). Viscosity was monitoredat ½ h intervals for the initial 2 h and subsequently 1 h intervals inorder to compare viscosity profiles of the unencapsulated vs.encapsulated breaker systems. Viscosity measurements were recorded on aBrookfield Digital Viscometer (Model DV II), spindle #4 at a motor speedof 20 RPM, and are compared to a control sample that has been exposed tothe same temperature profile and which is identical in compositionexcept containing no breaker.

[0032] The above test does not duplicate conditions downhole, but rathershows lab reproducible data for comparison of effectiveness of theencapsulated breaker with unencapsulated breaker and controlcompositions. Actual conditions downhole, such as shear and pressure,will result in a breaking profile that provides a higher level ofdistinction between encapsulated and non-encapsulated breaker. Thus,while the laboratory test would suggest that only a minor benefit isprovided by encapsulating the breaker, a much longer benefit is actuallyobserved under conditions of use downhole.

[0033] The encapsulated breaker of the present invention is preferablyadded to the fracturing fluid before the fluid is pumped downhole. Inthe preferred aspect of the present invention, the encapsulated breakeris extremely stable even in the presence of water at ambient conditionsabove ground, so the mixing with the fracturing fluid can be taken withdue time and care without concern as to premature viscosity breakdown.Preferably, the encapsulated breaker is provided as a slurry, so that itmay be easily mixed with the fracturing fluid without the need to resortto solid metering devices. Most preferably, the slurry composition ofthe present invention is pumped simultaneously with the fracturing fluiddownhole using liquid metering devices. Optional liquid mixing equipmentto ensure even mixing of the two liquid streams may additionally beutilized.

[0034] The following examples are provided for purposes of illustratingthe present invention, and are not intended to be limiting of thebroadest concepts of the present invention. Unless otherwise indicated,all parts and percentages are by weight.

EXAMPLES Example 1

[0035] Preparation of Dry Encapsulated Breaker

[0036] A 500 mL unbaffled polymerization flask was charged with 350 MLof hexane, 40 g of industrial grade potassium persulfate (40-80 mesh)and 10 g ethyl-2-cyanoacrylate. The persulfate salt was dispersed bystirring at 1200 RPM with a 3-blade, marine style propellor. Afterstirring for about 10 minutes, 0.1 g of triethanolamine was added to thesuspension. Stirring continued at room temperature for a further twentyminutes at which time the product was collected by vacuum filtration ona Buchner funnel and air dried under ambient conditions. The dry productis a white, free-flowing powder.

Example 2

[0037] Preparation of Encapsulated Breaker Slurry Composition

[0038] A 1 L polymerization flask fitted with stainless steel baffleswas charged with 300 mL of IPAR 3 drill mud oil and 80 g of industrialgrade potassium persulfate (60-100 mesh). Over a period of ca. 20minutes, 15 g ethyl-2cyanoacrylate was added to the mixture. Thepersulfate salt was dispersed by stirring at 1500 RPM with a 6-bladeturbine agitator. After stirring for ca. 10 minutes, 0.1 g oftriethanolamine was added to the suspension. Stirring continued at roomtemperature for a further twenty minutes to ensure complete reaction ofthe cyanoacrylate. With continued stirring, 17 g of “Cab-O-Sil M-5”Silicon Dioxide was added to the mixture in order to provide a stableslurry of the coated persulfate particles.

DETAILED DESCRIPTION OF THE DRAWING

[0039]FIG. 1 is a photograph of two vials of encapsulated breakercompositions in water. Vial A contains encapsulated breaker of theinvention (Example 1). Vial B contains encapsulated breaker coatedwithin a polymer that does not hydrolytically degrade. These vials havenot been heated.

[0040]FIG. 2 is a photograph of the vials of FIG. 1 after heating to atemperature of 80° C. for 2.5 hours. These photographs demonstrate thatthe capsule shell of the present invention hydrolytically degrades uponexposure to heat in the presence of water, thereby dissolving thecapsule shell wall and reducing the amount of solid material to berecovered from the subterranean formation during the petroleum recoveryoperation.

[0041]FIG. 3 is a graphical representation of the Standard BreakingTest, except that the viscosity measurements are carried out at 60° C.Line A represents the time/viscosity profile of a Control sample ofcrosslinked guar, i.e. containing no breaker. Viscosity is reduced to anessentially stable level after about one hour. Line B represents thetime/viscosity profile of a sample of crosslinked guar comprisingunencapsulated breaker. This sample exhibits relatively rapid viscositybreakdown, even under laboratory conditions where no pressure or shearforces are present in the manner that would be experienced under actualconditions of use. Line C represents the time/viscosity profile of asample of crosslinked guar comprising encapsulated breaker that has beenmixed into the guar from the dry form (per example 1 above). This sampleexhibits a relatively slower viscosity breakdown as compared to theunencapsulated breaker, even under laboratory conditions. Thus,viscosity breakdown is delayed at least 20 minutes as compared tounencapsulated breaker. Line D represents the time/viscosity profile ofa sample of crosslinked guar comprising encapsulated breaker that hasbeen mixed into the guar from a slurry (per example 2 above). Thissample exhibits an even slower relative viscosity breakdown as comparedto the unencapsulated breaker. Thus, viscosity breakdown is delayed atleast 60 minutes as compared to unencapsulated breaker.

1. An encapsulated breaker comprising a breaker capable of reducing theviscosity of a fracturing fluid enclosed within a hydrolyticallydegradable coating.
 2. The encapsulated breaker of claim 1 , whereinsaid coating is formed from a composition comprisingpoly(alkyl-2-cyanoacrylate).
 3. The encapsulated breaker of claim 2 ,wherein said coating is formed from a composition additionallycomprising one or more comonomers that are copolymerizable withalkyl-2-cyanoacrylate.
 4. The encapsulated breaker of claim 3 , whereinsaid comonomers are selected from the esters of acrylic acid andmethacrylic acid.
 5. The encapsulated breaker of claim 3 , wherein saidcomonomers are selected from the group consisting of acrylic ormethacrylic esters of non-tertiary alcohols, which alcohols are selectedfrom the group consisting of ethanol, 1propanol, 2-propanol, 1-butanol,2-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2methyl-1-butanol,1-hexanol, 2-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol,2-ethyl-1-butanol, 3,5,5-trimethyl-1-hexanol, 3-heptanol, 1-octanol,2-octanol, isooctanol, 2-ethyl-1-hexanol, 1-decanol, 1-dodecanol,1-tridecanol and 1-tetradecanol or mixtures thereof.
 6. The encapsulatedbreaker of claim 3 , wherein said comonomers are selected from the groupconsisting of acrylamides and styrenes.
 7. The encapsulated breaker ofclaim 2 , wherein said coating is formed from a composition comprisingat least about 50% by weight of poly(alkyl-2cyanoacrylate) based on thetotal weight of the coating.
 8. The encapsulated breaker of claim 2 ,wherein said coating is formed from a composition comprising at leastabout 70% by weight of poly(alkyl-2-cyanoacrylate) based on the totalweight of the coating.
 9. The encapsulated breaker of claim 2 , whereinsaid coating is formed from a composition comprising at least about 90%by weight of poly(alkyl-2cyanoacrylate) based on the total weight of thecoating.
 10. The encapsulated breaker of claim 2 , wherein the alkylgroup of poly(alkyl-2-cyanoacrylate) is C1-20 alkyl.
 11. Theencapsulated breaker of claim 2 , wherein the alkyl group ofpoly(alkyl-2-cyanoacrylate) is C1-6 alkyl.
 12. The encapsulated breakerof claim 1 , wherein said breaker comprises a persulfate salt.
 13. Theencapsulated breaker of claim 12 , wherein said persulfate salt ispotassium persulfate.
 14. A breaker slurry composition comprising aslurry of encapsulated breaker of claim 1 in an organic solvent.
 15. Theslurry composition of claim 14 , wherein said organic solvent ispredominantly aliphatic.
 16. The slurry composition of claim 14 ,wherein said organic solvent comprises kerosene.
 17. The slurrycomposition of claim 14 , wherein said organic solvent comprises mineraloil.
 18. The slurry composition of claim 14 , wherein said organicsolvent comprises a blend of one or more hydrocarbons.
 19. The slurrycomposition of claim 14 , comprising one or more surfactants.
 20. Theslurry composition of claim 19 , wherein said surfactant is selectedfrom the group consisting of oxyalkylated phenolic resin surfactants,resin ester surfactants, polyol surfactants, alkylaryl sulfonatesurfactants, polymeric amine surfactants, alcohol ether sulfonates,imidazoline cationic surfactants, complex phosphate esters, aminealkylaryl sulfonates, alkyl amidoamine surfactants, polyamidoimidazoline surfactants, fatty imidazoline surfactants, dimer trimeracid surfactants, polyoxyethylated rosin amines, polyoxyethylated rosinamines, polyoxyethylene glycol surfactants, alcohol ether sulfonatesurfactants, alcohol ether sulfate surfactants, sulfonate surfactants,sodium alpha olefin sulfonates, sodium alcohol ether sulfates, calciumalkylaryl sulfonates, amine dodecylbenzene sulfonates, fatty acidamides, alkanolamides, fluorinated surfactants, and mixtures thereof.21. An encapsulated breaker comprising a breaker capable of reducing theviscosity of a fracturing fluid, said breaker enclosed within ahydrolytically degradable polymer coating wherein said encapsulatedbreaker does not reduce viscosity lower than 50% at 5 hours at 25° C. ina Standard Breaking Test, but said encapsulated breaker does not reduceviscosity lower than 50% at 70° C. at a first predetermined timeselected between fifteen minutes and 12 hours, but does reduce viscositylower than 50% at a second predetermined time period selected betweenfifteen minutes and 12 hours after said first predetermined time at 70°C. in a Standard Breaking Test and wherein said encapsulated breakerreduces viscosity lower than 50% in a Standard Breaking Test at least 20minutes after a like composition where the breaker is not encapsulated.22. The encapsulated breaker of claim 21 , wherein said firstpredetermined time is between about 1 and 3 hours and said secondpredetermined time period is between about 3 and 5 hours.
 23. A methodof breaking a fracturing fluid comprising introducing an encapsulatedbreaker of claim 1 into a subterranean formation being treated with thefracturing fluid and exposing said breaker to temperatures in excess ofabout 40° C., thereby hydrolytically releasing said breaker.
 24. Themethod of claim 23 , wherein said encapsulated breaker is provided as aslurry.
 25. Method of manufacturing encapsulated breaker comprising: a)suspending a solid breaker particle in a reaction solution comprisingnon-aqueous solvent and an effective amount of (alkyl-2-cyanoacrylate),b) adding weak base in an amount effective to initiate polymerization ofthe (alkyl-2-cyanoacrylate).
 26. The method of claim 25 , furthercomprising the step of filtering said encapsulated breaker from thenon-aqueous solvent.
 27. The method of claim 25 , wherein saidalkyl-2-cyanoacrylate comprises about 1-20% by weight of the reactionsolution.